The goal of this research is to gain a better understanding of the mechanisms required for synaptic transmission. I will accomplish this by characterizing a novel gene identified in a Drosophila screen for mutants defective in neuronal communication. I have completed the mapping of over 130 mutants with large and small deficiencies and have assigned them to 33 separate complementation groups. The gene I will study is defined by a complementation group with 20 alleles. I chose this gene because the mutants have completely normal morphology both grossly and microscopically, yet have abnormal neuronal function based on two physiological assays. Mutations in this gene are lethal, further suggesting an essential role in neuronal function. I will first complete the fine mapping to identify this gene and characterize the mutations molecularly. Then I will analyze the gene's expression pattern and the protein's subcellular localization. Finally I will perform a thorough characterization of the gene's role in neuronal function using electrophysiology, dye uptake studies, and transmission electron microscopy. This work will contribute to our understanding of neurotransmission. In the process I will gain valuable experience in Drosophilo genetics, molecular biology, and assays for neuronal function